1. Field of the Invention
The present invention relates to an optical information recording disc and a disc drive apparatus, and more particularly to an engagement device for transmitting the power of a spindle provided within a disc drive apparatus to an optical information recording disc without fail.
Description of Related Art
There have been known two kinds of clamping systems for optical information recording discs, i.e., a mechanical clamp system and a magnetic clamp system.
In the mechanical clamp system, as shown in FIG. 22, a clamp member 42 is disposed so as to confront a spindle 41, and an optical information recording disc 43 is loaded on the spindle 41. Thereafter, the clamp member 42 is lowered to press the optical disc 43 by a spring force of a spring 44.
On the other hand, in the magnetic clamp system, as shown in FIG. 23, a magnet 46 is embedded in a turntable 45 formed integrally with a spindle 41, and magnetic members 47 are disposed close to a central portion of an optical information recording disc 43, so that the optical disc 43 is clamped by a magnetic attraction force between the magnet 46 and the magnetic members 47.
In the mechanical clamp system of the conventionally well known clamp systems, it is necessary to provide the clamp member 42 and a member for driving the clamp member. As a result, the disc drive mechanism becomes expensive. Also, since it is necessary to provide a large space for the arrangement of the clamp member 42 and the like, the disc driving device is enlarged in size.
The magnet clamp system does not suffer from the above-described disadvantages. However, in the magnetic clamp system, since the optical information recording disc 4 is clamped only by the magnetic attraction force between the magnet 46 and the magnetic member 47 and the friction between the turntable 45 and the magnetic members 47, the clamping force is relatively weak. As a result, when the spindle 41 is started to be operated at a high speed or when the optical disc 43, lacking dynamic balance, is driven rotatably at a high speed, undesired slippage occurs between the optical disc 43 and the turntable 45, so that a rotation jitter is increased to cause a recording/reproducing error or to cause a data transfer speed to be lowered.
Accordingly, in the technical field of the optical information recording disc and the disc driving apparatus, is important to the above-described technical disadvantages.